Two-quasiproton states in 168Er studied by the 169Tm(t, α)168Er reaction

The ${}^{169}\text{Tm}\text{(}\text{t}\text{, α)}{}^{168}\text{Er}$ reaction has been studied using 17 MeV polarized tritons from the Los Alamos National Laboratory tandem Van de Graaff accelerator. The α-spectra were analyzed with a Q3D magnetic spectrometer. The overall energy resolution was typically ~ 15 keV (FHWM) and angular distributions of cross sections and analyzing powers were obtained for levels up to ~ 2.7 MeV. The fact that spins and parities for all levels up to ? 2 MeV were previously known from an extensive series of (n, γ) studies made it possible to determine specific two-quasiproton structures for many bands from the present results. The K^π = 2⁺ γ-vibrational band was found to have a large $\text{3}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}\text{+}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}$ admixture, consistent with the predicted microscopic composition of this phonon, but no $\text{5}\text{2}\text{[413]}{}_{\mathrm{<mtext>p</mtext>}}\text{?}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}$ component was observed. The K^π = 0₄⁺ band at 1833 keV has ～ 25% of the $\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}\text{?}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}$ two-quasiproton strength. This is in excellent agreement with the Soloviev model but is inconsistent with the interacting boson model, in which the K^π = 0₄⁺ band is composed almost completely of multiphonon configurations that should not be populated in a single-nucleon transfer reaction. The $\text{K}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{?}}\text{,}\text{7}\text{2}{}^{\mathrm{?}}\text{[523]}{}_{\mathrm{<mtext>p</mtext>}}\text{+}\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}{}_{\mathrm{<mtext>p</mtext>}}$ two-quasiproton and the $\text{K}{}^{\mathrm{\pi }}\text{= 4}{}^{\mathrm{?}}\text{,}\text{7}\text{2}{}^{\mathrm{+}}\text{[633]}{}_{\mathrm{<mtext>n</mtext>}}\text{+}\text{1}\text{2}{}^{\mathrm{?}}\text{[521]}{}_{\mathrm{<mtext>n</mtext>}}$ two-quasineutron states are mixed strongly with each other, but the two K^π = 3^? bands composed of antiparallel couplings of the same particles are not. A good qualitative explanation of this mixing pattern is provided in terms of the effective neutron-proton interaction.     

Observation of proton emission following thermal neutron capture in 34.5 d 84Rb

Using a target prepared by on-line isotope separation, thermal neutron capture in ⁸⁴Rb (I^π = 2^?) has been shown to induce proton emission to the ground state (0⁺) and first excited state (2⁺) of ⁸⁴Kr. The branching ratio was measured as $\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{(0}{}^{\mathrm{+}}\text{)}\text{Γ}{}_{\mathrm{<mtext>p</mtext>}}\text{(2}{}^{\mathrm{+}}\text{)}\text{= 4.7 ± 0.7}$, favouring a $\text{3}\text{2}{}^{\mathrm{?}}$ assignment of the capturing state without excluding $\text{5}\text{2}{}^{\mathrm{?}}$, and the (n_th, p) cross section as 12 ± 2 b. The energy available for the process was determined to be 3.45 ± 0.01 MeV, in agreement with other mass data in the region.     

Single-proton states in 151Pm

The ${}^{152}\text{Sm}\text{(}\text{t}\text{, α)}{}^{151}\text{Pm}$ reaction was studied using 17 MeV polarized tritons from the tandem Van de Graaff accelerator at the Los Alamos Scientific Laboratory. The α-particles were analyzed using a Q3D magnetic spectrometer and detected with a helical-cathode position-sensitive counter. The overall resolution was ～ 18 keV FWHM. Measurements of the ¹⁵⁰Nd(³He, d)¹⁵¹Pm reaction were made using 24 MeV ³He beams from the McMaster University tandem accelerator. The deuteron spectra were analyzed with a magnetic spectrograph using photographic emulsions for detectors, yielding a resolution of ～ 13 keV FWHM. By comparing the measured angular distributions of ($\text{t}\text{, α}$) and (³He, d) cross sections and ($\text{t}\text{, α}$) analyzing powers with DWBA predictions it was possible to assign spins and parities to many levels. The present results confirm earlier assignments of rotational bands based on the low-lying $\text{5}\text{2}{}^{\mathrm{+}}\text{[413],}\text{5}\text{2}{}^{\mathrm{?}}\text{[532],}\text{3}\text{2}{}^{\mathrm{+}}\text{[411]}\text{and}\text{1}\text{2}{}^{\mathrm{+}}\text{[420]}$ orbitals. In addition, states at higher excitation have now been assigned to the $\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}\text{and}\text{7}\text{2}{}^{\mathrm{+}}\text{[404]}$ orbitals, and members of the $\text{3}\text{2}{}^{\mathrm{+}}\text{[422],}\text{5}\text{2}{}^{\mathrm{+}}\text{[402],}\text{3}\text{2}{}^{\mathrm{?}}\text{[541]}\text{and}\text{7}\text{2}{}^{\mathrm{?}}\text{[523]}$ bands are tentatively proposed. The spectroscopic strengths can be explained reasonably well by the Nilsson model when pairing and Coriolis mixing effects are included.     

Electromagnetic transitions in 42Ti

Levels in ⁴²Ti up to 4 MeV have been investigated using the ⁴⁰Ca(³He, n)⁴²Ti reaction and a neutron time-of-flight method. Using the DSA method, lifetimes of 750±300, > 200, 350±250, > 2000 and < 250 fs have been measured for levels at E_x = 1.56, 1.85, 2.40, 2.68 and 3.74 MeV respectively. The level at E_x = 3043.0±1.5 keV is tentatively identified as the 6⁺ member of the $\text{(f}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}{}^2$ configuration, and its mean life has been measured as 26±5 ns by a direct timing method. Using isospin formalism, transition strengths are compared with theoretical and experimental values for ⁴²Ca and ⁴²Sc.     

Neutron-proton radius differences and isovector deformations from π+ and π− inelastic scattering from 18O

π⁺ and π^? elastic and inelastic scattering from ¹⁸O have been measured at T(π)=164 MeV. Consistent with the results at 230 MeV, it is found that the ratio $\text{σ(π}{}^{\mathrm{?}}\text{)}\text{σ(π}{}^{\mathrm{+}}\text{)}$ for the 2₁⁺ state is 1.86(16), while for the 3₁^? state it is 0.89(6). These results are interpreted as indicating differences in neutron and proton deformations characterizing the 2₁⁺ transition and partial neutron blocking for the 3₁^? transition. Optical model analysis of elastic scattering leads to the conclusion that $\text{〈r}{}_{\mathrm{<mtext>n</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?〈r}{}_{\mathrm{<mtext>p</mtext>}}{}^2\text{〉}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{=0.03(3)}\text{fm}$.     

An experimental investigation of the radiative structure decay K+ → e+υγ

The decay K⁺ → e⁺υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD₊) the branching ratio $\text{Γ(}\text{SD}{}_{\mathrm{+}}\text{)}\text{Γ(}\text{K}{}_{\mathrm{\mu 2}}\text{) = (2.33 ± 0.42) × 10}{}^{\mathrm{?5}}$ is obtained from 51 ± 3 events observed in the kinematical region E_e ? 235 MeV, E_γ > 48 MeV and θ_eγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD_?)/Γ(SD₊) < 11 (90% CL) from the sample of electrons with energies 220 MeV ? E_e < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region $\text{?1.8 < a}{}_{\mathrm{<mtext>K</mtext>}}\text{υ}{}_{\mathrm{<mtext>K</mtext>}}\text{< ?0.54}$.For the decay $\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}$ the limit $\text{Γ(}\text{K}{}^{\mathrm{+}}\text{→}\text{e}{}^{\mathrm{+}}\text{νν}\text{ν}\text{)/Γ(}\text{K}{}_{\mathrm{e2}}\text{) < 3.8}$ 90% confidence level) was found.     

Accurate determination of the 17O16O + n coupling constant and spectroscopic factor

We have measured ¹⁶O¹⁷O elastic cross sections at 22 MeV between 65°–140° to ± 1 %. The observed oscillatory interference between Coulomb scattering and the neutron transfer process is analyzed using exact finite-range DWBA. A model-independent value of $\text{C}\text{?}{}^2\text{= 0.82 ± 0.07}$ is obtained for the coupling constant of the 1d_{$\text{5}\text{2}$} neutron in ¹⁷O. We also present an analysis of data on magnetic electron scattering from ¹⁷O, which yields precise information on the magnitude and the radial shape of the $\text{1}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ neutron bound-state wave function. With this we relate the coupling constant to the spectroscopic factor and find S = 1.04 ± 0.11. We show that the magnetic electron scattering data alone yield S = 1.04 ± 0.10. Combining these results with earlier work we recommend $\text{C}\text{?}{}^2\text{= 0.79 ± 0.04}$ and S = 1.03 ± 0.07 as best values. This spectroscopic strength corresponds to (91 ± 7) % of the full single-particle value.     

Backward-angle high-resolution inelastic electron scattering on 40, 42, 44, 48Ca and observation of a very strong magnetic dipole ground-state transition in 48Ca

The search for magnetic dipole transitions from the ground state-even Ca isotopes to high lying J^π=1⁺ states by means of low momentum transfer but high resolution inelastic electron scattering is described. The previously detected strongly excited J^π=1⁺ state E_X=10.319 MeV [B(M1)↑=1.12±0.27μ_K²] in ⁴⁰Ca has been confirmed, but - contrary to the expectations of the independent particle shell model - only a fairly weak M1 transition is observed in ${}^{42}\text{Ca [E}{}_{\mathrm{<mtext>X</mtext>}}\text{= 11.235}\text{MeV}\text{, B(}\text{M}\text{1)↑=0.59±0.05 μ}{}^2{}_{\mathrm{<mtext>K</mtext>}}\text{]}$ and none in ⁴⁴Ca between E_{X=8.2?12.2 MeV}. In ⁴⁸Ca, however, a very strong M1 transition [B(M1) ↑ = 4.0 ± 0.3 μ²_K] to a single state at E_X=10.227 MeV has been discovered.     

The rotational bands 12+[411]and 12−[541]in 175Lu

In a study of the γ-radiation emitted in the reaction ¹⁷⁶Yb(p, 2n) excited states of the nucleus ¹⁷⁵Lu up to spin I = $\text{13}\text{2}$ have been investigated. The main results concern the rotational bands $\text{1}\text{2}$⁺ [411]and $\text{1}\text{2}$^? [541]with the corresponding band heads found at 626.60 and 370.88 keV, respectively. The half-life of the $\text{1}\text{2}$⁺[411] level has been determined to be $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 10.7±0.5}\text{ns}$. Furthermore, the band heads $\text{3}\text{2}$^?[532]and $\text{3}\text{2}{}^{\mathrm{+}}$[411]are proposed at energies of 999.0 and 1150.8 keV, respectively. Experimental E1 transition probabilities between both $\text{K =}\text{1}\text{2}$ bands are compared with calculations including the Coriolis and pairing effects, as well as theoretically deduced quadrupole deformation parameters.     

Study of low-lying states in 92Tc with the 92Mo(3He,t) reaction

States in ⁹²Tc have been studied by means of the ⁹²Mo(³He, t) reaction at 27.5 MeV. The Q-value for this reaction and the excitation energy of the isobaric ground state analogue of ⁹²Mo were determined to be ?7.882 ± 0.030 MeV and 3.813 ± 0.030 MeV respectively. Strongly populated levels in ⁹²Tc appear to belong to configurations arising from the $\text{(1g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{\pi }}\text{(1g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{\nu }}{}^{\mathrm{?1}}$ multiplet.     

Study of the levels in 167Tm by the 165Ho(α, 2nγ)167Tm reaction

Gamma-ray spectra following the ¹⁶⁵Ho(α, 2n)¹⁶⁷Tm reaction have been studied using different semiconductor detector systems including a Compton suppression spectrometer. Approxi- mately 400 transitions have been observed in the energy range 60 to 1250 keV and 4 × 10⁷ γγ coincidence events have been recorded. The angular distributions of the more intense γ-rays have been determined. The level scheme of ¹⁶⁷Tm has been extended in several respects: The four previously known rotational bands based on the Nilsson orbitais $\text{1}\text{2}{}^{\mathrm{+}}\text{[411]}$, $\text{7}\text{2}{}^{\mathrm{+}}\text{[404]}$, $\text{7}\text{2}{}^{\mathrm{?}}\text{[523]}$ an $\text{1}\text{2}{}^{\mathrm{?}}\text{[541]}$ have been extended up to spin values $\text{31}\text{2}$, $\text{31}\text{2}$, $\text{31}\text{2}$, $\text{33}\text{2}$ respective based on the $\text{3}\text{2}{}^{\mathrm{+}}\text{[411]}$ and $\text{5}\text{2}{}^{\mathrm{+}}\text{[402]}$ orbitals have been established for which only few levels were known previously. Finally two hitherto unknown rotational bands have been found for which we propose the assignments $\text{{}\text{7}\text{2}{}^{\mathrm{+}}\text{[404]; K + 2}}$ and $\text{3}\text{2}{}^{\mathrm{?}}\text{[532] + {}\text{1}\text{2}{}^{\mathrm{?}}\text{[541]; K?2}}$. Coriolis coup calculations are presented. The value of $\text{(1?δ}{}_{\mathrm{<mtext>K,\; </mtext><mtext>1</mtext><mtext>2</mtext>}}\text{b}{}_0\text{) (g}{}_{\mathrm{K}}\text{?g}{}_{\mathrm{R}}\text{)/Q}{}_0$ was determined for three bands from branching ratios and from angular distributions.     

Evidence for two narrow pp resonances at 2020 MeV and 2200 MeV

From the study of the reaction $\text{π}{}^{\mathrm{?}}\text{p→p}{}_{\mathrm{F}}\text{p}\text{p}\text{π}{}^{\mathrm{?}}$ using a fast proton (p_F) trigger device in the CERN Omega spectrometer, we find evidence for two narrow $\text{p}\text{p}$ states produced mainly in association with a Δ° (1232) and a N° (1520). The statistical significance of each peak is greater than 6 standard deviations. Masses and natural widths of these resonances are respectively M = 2020 ± 3 MeV, Λ₁ = 24 ± 12 MeV and M₂ = 2204 ± 5 MeV, Λ₂ = 16_?16⁺²⁰ MeV. Our data are consistent with a small production of the narrow ～ 1935 MeV resonance already reported. Production cross sections for these new $\text{p}\text{p}$ resonances are given.     

On the 18O positive-parity rotational band

Deuteron-alpha angular correlations have been measured for the reaction ${}^{14}\text{C}\text{(}{}^6\text{Li,d}\text{)}{}^{18}\text{O}{}^1\text{→α}{}_0\text{+}{}^{14}\text{C at}\text{E(}{}^6\text{Li}\text{)=34}\text{MeV}$ and θ_d^lab=10°. Transitions involving the 11.69 MeV (6⁺) and the 17.6±0.2 MeV ¹⁸O states have been analyzed. Spin and parity are confirmed for the known 11.69 MeV (6⁺) state and assigned to be 8⁺ for the 17.6 MeV level. This last is suggested to be the fifth member of the positive-parity ¹⁸O rotational band built on the 3.63 MeV (0⁺) level.     

Stroboscopic observation of quadrupole hyperfine interactions

A stroboscopic technique for the observation of quadrupole hyperfine interactions of isomeric nuclear states has been successfully developed. The inherent precision and resolution of this technique have been demonstrated by measuring the quadrupole hyperfine frequency for ${}^{69}\text{Ge(}\text{9}\text{2}{}^{\mathrm{+}}{}_1\text{, τ = 4.0μ)}$ in Zn metal at several temperatures; ω₀ = [19.67 ± 0.06] × 10⁶s^?1 (at 623 ± 3 K).     

X-ray compressibility measurements of the graphite intercalates KC8 and KC24

The isothermal compressibilities of pristine graphite and stages 1 and 2 potassium-graphite have been measured at room temperature. Diamond anvil X-ray diffraction techniques were employed to determine the c-axis lattice constant as a function of hydrostatic pressure up to 12 kbar. The compressibilities $\text{k}{}_{\mathrm{c}}\text{?}\text{1}\text{C}{}_{33}$ were found to be (2.73±0.09)×10^-12, (2.13±0.09)×10^-12, (5.3±0.8)×10^-12 and $\text{(1.6±0.2)×10}{}^{-12}\text{cm}{}^2\text{dyn}$ for graphite, KC₈, stage 2 KC₂₄ and stage 3 KC₂₄, respectively. The compressibility of KC₈ was comparable to that of RbC₈ deduced from neutron scattering experiments.     

Generalization of multiperipheral model with long range correlations; Van Der Waals approximation

Three enhancements are observed in the final state ω^°π⁺π⁺π⁺⁺π^?π^? selected from the channel $\text{p}\text{p → 3π}{}^{\mathrm{+}}\text{3π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{°}}$ at 715 MeV/c: one in ω^°π^± at 1040 MeV (～ ≈ 55MeV) ω^°π⁺π^?, respectively near 1315 MeV (～ ≈ 100 MeV) and 1405 MeV (～ ≈ 40 MeV). The first two effects are strongly correlated and are interpreted in terms of a sequential decay A^°₂ through a new object, the B₁. The second (ωππ) enhancement seems to be an ?^°?^° effect below threshold and is attributed to a pionic decay of the $\text{K}\text{K}\text{)}{}_{\mathrm{I}}\text{=1}$ effect seen around the same mass in other reactions.     

Two-step processes in the 40Ca(α, 3He)41Ca reaction

The ⁴⁰Ca(α, ³He) reaction has been studied at 36 MeV incident energy. About fifty levels have been observed up to 7.1 MeV excitation energy and angular distributions were measured from 6–60° using a split-pole spectrometer. A local zero-range DWBA analysis has been carried out, and the deduced l-assignments and spectroscopic factors are compared with those obtained from previous neutron stripping experiments. Core-excited states in ⁴¹Ca with a [3^? ? f_7,2], [2⁺ ? f_7,2] and [5^? ? f_7,2] component previously observed in inelastic scattering experiments, are selectively excited by the (α, ³He) reaction. Their angular distributions are compared with coupled-reaction-channel calculations, assuming a pure two-step reaction mechanism. The agreement between theory and experiment may be considered as rather satisfactory for a number of levels. In particular the $\text{1}\text{2}{}^{\mathrm{+}}\text{and}\text{3}\text{2}{}^{\mathrm{+}}$ levels and the high-spin states with $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{?}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{,}\text{15}\text{2}{}^{\mathrm{+}}\text{and}\text{17}\text{2}{}^{\mathrm{+}}$ are successfully described within the framework of the weak-coupling model.